1. Technical Field
The present invention relates generally to an optical network termination having the function of: detecting and recovering from failures, blocking supplied power, and storing information. More particularly, the present invention relates to an optical network termination system functioning to detect any abnormal optical output using only a microprocessor installed on an uplink, to perform recovery from an abnormality, to block power to an optical module, to store information in a storage medium and to display the information on an external device when a continuous optical output of an optical module is generated to cause an Optical Network Terminal (hereinafter referred to as ONT) to obstruct internet services for another ONT.
Also, the present invention relates to a method for the detection of continuous optical output, the recovery from failures, and the blockage of continuous optical output. More particularly, the present invention relates to a method for detecting a continuous optical output using a failure detection/recovery/blockage microprocessor which functions to determine that an optical module is operating normally when recognizing a section where detected signals of a continuous optical monitor diode (mPD) have a low value for a predetermined time period, or can reset or block the optical module when an abnormal continuous optical output state having high values is detected.
2. Description of the Related Art
In general, a Passive Optical Network (hereinafter referred to as “PON”) consists of one Optical Line Termination (hereinafter referred to as “OLT”) at the service provider's central office and a number of Optical Network Terminals or Optical Network Units (hereinafter referred to as ONTs) near end users. In this PON, a number of ONTs may transmit optical signals to the OLT, that is, may transmit uplink data only for a period of time that is allocated to them.
If at least one of the ONTs transmits optical signals to the OLT other than at or beyond a time period allocated to it, a collision is highly likely to occur due to simultaneous optical signal transmission of other ONTs, causing communication failure of the entire network.
Below, a description will be given of an situation in a conventional art where one ONT has a failure that may result in a subsequent failure of the entire network.
As illustrated in FIG. 1a, a PON system 2 is a telecommunication network in which a optical subscriber network is constructed to provide optical network-based high-speed communication services to corporate or home users, thus allowing for access to multiple ONTs 30-1 through 30-n with one OLT 10 using a passive optical device, splitter 20.
PON system 2 includes TDM-PON using a Time Division Multiplexing (TDM) protocol and WDM-PON using a Wavelength Division Multiplexing (WDM) protocol. A PON system 10 of a Time Division Multiplexing method includes ATM-PON using Asynchronous Transfer Mode (ATM). Ethernet-based E-PON, G-PON using common frame protocol, etc.
The PON system 2 using a Time Division Multiplexing protocol operates as described below. In a downstream direction in which data is transferred from an OLT 10 to ONTs 30-1 through 30-n, the OLT 10 inserts and sends registered identifiers of ONTs 30-1 through 30-n into a preamble of frames and ONTs 30-1 through 30-n receive only those frames having their own identifiers. However, as illustrated in FIG. 1b, in an upstream direction in which data is transferred from ONTs 30-1 through 30-n to OLT 10, OLT 10 allocates time slots of an upstream transmission process to all of the ONTs 30-1 through 30-n, and individual ONTs 30-1 through 30-n may transmit data to OLT 10 only for the respective time slot allocated to each of them individually.
In the upstream process mentioned above, as illustrated in FIG. 1c, when an ONT 10 has a defect of causing a laser diode to be in a constantly illuminated state, there could be a problem that as the defective ONT 30-1 blocks the subsequent time slots of the upstream process, it not only prevents a plurality of other ONT 30-2 through 30-n from sending data to the OLT 10, but also causes the OLT 10 to determine that ONT 30-2 through 30-n, having no defects, are not functioning properly.
Accordingly, the present invention intends to allow streamlined operation of the PON system 2 via the early detection of a constantly illuminated state of a laser diode of a defective ONT 30, and shutting down the optical module of the defective ONT 30.
The ONT 30 may include an optical transmitter module 32, an optical receiver module 34, and a control unit 36.
The optical transmitter module 32 sends optical signals to the OLT 10 according to the orders of the control unit 36. The optical transmitter module 32 may consist of a laser diode, emitting optical signals, and a laser driver unit to drive the laser diode. The optical receiver module 34 receives optical signals from the OLT 10. The optical receiver module 34 can be implemented as a module together with the optical transmitter module 32. The control unit 36 is able to carry out a function to disconnect the optical transmitter module 32 according to the order of suspending optical signals from the OLT 10.
OLT 10 may include an optical transmitter module 12, an optical receiver module 14, and a control unit 36.
An optical transmitter module 12 receives optical signals from multiple ONUs 30. The optical transmitter module 12 may include a photodiode for receiving optical signals and converting them into electrical signals and an amplifier for amplifying the converted signals. A control unit 36 provides transmitted data and photoactive signals to the optical transmitter module 12 or receives and processes photoelectric-converted data of optical signals received from the optical receiver module 14 and generally controls the OLT 10.
A control unit 36 may further include a Received Signal Strength Indicator (hereinafter referred to as RSSI) 16a and a failure determination unit 16b. 
RSSI 16a detects received signal strength of the received optical signals. A failure determination unit 16b determines if the ONT 30-1 is in an abnormal state. The failure determination unit 16b compares an optical power level detected by RSSI 16a with a reference value and determines that ONT 30-1 is in a normal state if the optical power level does not exceed the reference value, or is in an abnormal state if the optical power level exceeds the reference value.
Here, if the optical power level is assumed to be a set of optical signal strengths of individual ONTs 30-1 through 30-n that share the same optical cable with the OLT 10, the reference value refers to an optical power level generated when an optical transmitter module 32 is in an illuminated state from one normal ONT 30-2. In other words, in a normal state, a received optical power level is maintained equivalently if ONT 30-1 has no defect, but the received optical power level increases to exceed the reference value due to a constant illumination of the abnormal ONT 30-1 when the ONT 30-1 has a defect.
When the failure determination unit 16b detects a failure, it transmits a failure message to the ONT 30-1 via the optical transmitter module 12 to resolve the failure. In addition, the individual ONTs 30 corresponding to it include a Transmitted Signal Strength Indicator (hereinafter referred to as TSSI).
As mentioned above, optical modules that indicate continuous optical output status through TSSI signals have been introduced, but the equipment installed on the high and low level systems is expensive and causes a total cost increase. In addition, conventional optical modules only store the number of failures or simply block the failures without any recovery attempt. Since they have no function of storing other types of failures such as the hang-up of a PON MAC chip, excessive voltage application, etc., it is not possible to identify causes of failures and it is difficult to quickly remedy failures.